Exemplary embodiments of the present invention relate to a method of correcting a defect in a mask used in a semiconductor device fabrication, and more particularly, to a method of correcting a defect in an extreme ultraviolet (EUV) mask.
As the integration density of semiconductor devices has increased in recent years, optical lithography has reached the limit. Small images have been transferred on a wafer by using resolution enhancement technologies, such as an optical proximity correction (OPC), a phase shift mask, an off-axis illumination, and so on. However, as semiconductor devices have become much finer, these technologies have reached the physical limit. Accordingly, much attention has been paid to a lithography which can transfer smaller images on a wafer. Immersion lithography has recently been proposed which increases a resolution by using a liquid medium having a higher refractive index than air. In addition, much research has been conducted on next generation lithography technologies which can ensure finer resolutions.
Representative examples of the next generation lithography technologies include an extreme ultraviolet lithography (EUVL), an electron projection lithography (EPL), a proximity electron-beam lithography (PEL), a proximity X-ray lithography (PXL), and so on. The EUVL is designed to use a wavelength of approximately 13.5 nm. Light having the wavelength of approximately 13.5 nm, however, is absorbed by most materials, including air. Thus, the EUVL uses reflective masks and reflective optical systems, instead of transmissive masks and transmissive optical systems.
FIG. 1 is a cross-sectional view schematically illustrating a sectional structure of an EUV mask used in a typical EUVL. Referring to FIG. 1, a multilayer reflection film 110 is disposed over a substrate (not shown). The multilayer reflection film 110 is formed by sequentially stacking materials 111 and 112 having different optical properties, and uses a constructive interference (Bragg reflection) of a partial reflection which occurs at the interface of the materials 111 and 112. The reflectivity of the multilayer reflection film 110 is proportional to the square of the difference between the refractive indexes (real parts of complex refractive indexes) of the two materials 111 and 112 which are alternately stacked. In addition, the wavelength and maximum reflectivity of the reflected extreme ultraviolet light are determined by the kinds of the materials 111 and 112. For example, when the multilayer reflection layer 110 has a structure in which molybdenum (Mo) 111 and silicon (Si) 112 are alternately stacked, its maximum reflectivity ranges from approximately 60% to approximately 75%. A capping layer 120 is disposed over the multilayer reflection film 110 and protects the multilayer reflection film 110. As one example, the capping layer 120 may include a silicon oxide (SiO2) film or a silicon (Si) film. A pattern structure in which a buffer pattern 130 and an absorption pattern 140 are sequentially stacked is disposed over the capping layer 120. As one example, the buffer pattern 130 may include a silicon oxide (SiO2) film, and the absorption pattern 140 may include a tantalum (Ta)-based absorber, such as a tantalum nitride (TaN) film, or a chromium (Cr)-based absorber.
When the lithography is performed using the EUV mask, an important issue is whether or not there is a defect in the multilayer reflection film 110. When there is a defect in the multilayer reflection film 110, the defect causes the variation in the intensity of a reflected light, resulting in a defective device. The defect of the multilayer reflection film 110 may be caused during the deposition of the multilayer reflection film 110, or may be caused by a defect of the capping layer 120. The defect of the capping layer 120 may be residual materials remaining on the surface of the capping layer 120 after an etching process is performed for forming the capping layer 120, or may be a defect of the capping layer 120 in itself. Thus, the defect of the capping layer 120 must be removed.
Generally, the defect of the capping layer 120 may be removed by a method using e-beam, focused ion beam (FIB), or atomic force microscope (AFM). However, since the method using e-beam or focused ion beam (FIB) utilizes equipments which use high energy, it is highly likely to cause another defect in the capping layer 120. Also, the method using atomic force microscope (AFM) is highly likely to cause another defect in the capping layer 120 because of its physical scratch operation. Moreover, as patterns have become fine below a certain size, for example, 20 nm or less, slight defects having been neglected must also be removed.
However, it is difficult to apply the existing methods due to their low resolution.